On-Axis Listening from the Sweet Spot; Why It's Important.

[Bob Rapoport]

The Human Ear: Evolution’s Finest Instrument

Long before music was recorded or concerts were staged, our ancestors relied on their ears for
survival. On the open savannah, the faint crack of a twig or the rustle of grass could mean predator or
prey. Over millennia, the human auditory system evolved with astonishing precision, allowing us to
localize sounds — to pinpoint exactly where a noise was coming from, even in total darkness.

This ability to map sound in three-dimensional space is hardwired into us. Today, audiophiles benefit from
that same evolutionary gift. When we listen to a well-recorded piece of music, our ears and brain
naturally assemble a ‘soundstage,’ placing instruments and voices exactly where the recording
engineer intended. To unlock this experience, however, our speakers must be set up correctly.

The Power of On-Axis Listening

When your speakers are properly aligned — positioned at equal distances from your listening position
and aimed directly at your ears (on-axis) — so the sound arrive at your ears simultaneously. The music blossoms into a
holographic image between the two speakers, where guitars, vocals, drums, and keyboards each have
their own precise location. It feels less like sound from boxes and more like a live performance in your
living room.

Why Distance Matters

Listening position dramatically influences how you perceive stereo imaging. Imagine setting up your
speakers and chair so that you form an equilateral triangle — six feet apart, and you six feet back. In
this near-field arrangement, the direct sound from each speaker reaches your ears before any
reflections from the walls, ceiling, or floor. Because of this, your auditory system receives clean,
unblurred localization cues.

You hear instruments in their intended places, and the soundstage has
depth, focus, and realism. But if you sit much farther away, room reflections begin to arrive almost
simultaneously with the direct sound. These delayed reflections blur the image, smearing the fine
details. Instead of a precise, three-dimensional picture of the performers, you perceive a vague wash of
sound spread across the room — big, but unfocused

The Science of Sound Waves

When sound waves meet, their interaction is critical. If two waves arrive in phase, they reinforce one
another, creating a stronger, more pronounced signal. If they arrive out of phase, they cancel, leaving
dips and gaps in the sound. The ratio of direct sound to reflected sound ultimately determines whether
your music has pinpoint clarity or dissolves into ambiguity.

The Takeaway

The human ear is a marvel of evolution, designed to detect and localize sound for survival. By
respecting that design and setting up our speakers properly — on-axis, equidistant, and at a listening
position where direct sound dominates over reflections — we can experience the full measure of what
high-fidelity stereo is meant to deliver: a true-to-life, three-dimensional soundscape that brings us
closer to the music we love.

 

[gorman]

Still trying to figure out how to conjugate this with KEF's coaxial drivers. Lots of people recommend to place them off-axis to the main listening position.
What are your thoughts about that?

 

[Bob Rapoport]

Still trying to figure out how to conjugate this with KEF's coaxial drivers. Lots of people recommend to place them off-axis to the main listening position.
What are your thoughts about that?

The primary specification for all speakers is the frequency response, taken at 1 meter, on-axis, in an anechoic chamber or outside so there are no reflections. The further off-axis the measurement, the lower the output of those frequencies. Sound waves are omni-directional in the bass so it doesn't matter where you sit, however as you get into the mid-range, the soundwaves narrow and become directional, with the highest frequencies narrowing to beam about 2" wide. Sitting off-axis means you miss hearing the highest frequencies.

The reason that's important is that localization cues in the music are conveyed in the highest frequencies, its important that those frequencies are heard at your listening position ahead of the later arriving reflected sounds. When sitting off-axis, the sound is rolled off, increasing the arrival time of the reflected sounds, interfering with the localization cues.

KEF's uni-Q driver assembly does a good job of creating coherent soundwaves with less interference so you hear the localization cues in the music before the reflected sounds arrive. The only reason to turn the speakers off axis is if the highest frequencies are not flat, which no speaker manufacturer would do on purpose. There are a lot of speaker manufacturers who don't seem to know why audiophiles value the sweet spot for on-axis listening. The imaging is simply superior to off-axis performance. Its also critical that the sounds of both speakers arrive at your listening position simultaneously, equal in volume. If they dont, the speaker you're sitting closest too will be louder than the other one and you'll lose pinpoint precision imaging.

 

[Kal Rubinson]

It is a bit more complex than that. Measurement are not made just on axis but at all vertical and horizontal angles and the off-axis treble roll varies with frequency and angle somewhat differently in different speakers. Some speakers have wider dispersion at HF than others and the better ones have more even dispersion over wider frequency band. Some even have flatter FR off-axis than on. It is possible to sit off axis without any HF roll-off in some cases and benefit from a different interaction of the wider angle dispersion energy with the listener and with room boundaries.

In setting up speakers, I believe that on-axis listening (and measurement) should always be the starting point but not always the end point.

 

[Bob Rapoport]

It is a bit more complex than that. Measurement are not made just on axis but at all vertical and horizontal angles and the off-axis treble roll varies with frequency and angle somewhat differently in different speakers. Some speakers have wider dispersion at HF than others and the better ones have more even dispersion over wider frequency band. Some even have flatter FR off-axis than on. It is possible to sit off axis without any HF roll-off in some cases and benefit from a different interaction of the wider angle dispersion energy with the listener and with room boundaries.

In setting up speakers, I believe that on-axis listening (and measurement) should always be the starting point but not always the end point.

I really appreciate your perspective — and I agree that on-axis listening is always the best place to start. One thing worth remembering is that as frequency rises, wavelength shortens. That’s why bass radiates in all directions, while treble becomes much more directional, almost like a beam from a flashlight. It’s not just preference — it’s physics — and it’s what makes careful tweeter alignment so important for locking in that three-dimensional stereo image we all chase

 

[Kal Rubinson]

Yes, it's physics but it ain't the whole story.